(1) Field of the Invention
The present invention relates to information transmission from remote sensors mounted on a rotating shaft and more particularly to a portable, battery powered, instrumentation telemetry device, mounted on a rotating shaft. This device transmits a low frequency FM signal containing information obtained from the rotating shaft sensors without requiring a contact dependent coupling to the stationary platform which would restrict the shaft's radial or axial movement or contributing any unbalanced loads to the rotating shaft, especially at high shaft RPM's.
(2) Description of the Prior Art
Several methods have been used in the past to obtain real time information, such as torque, from a rotating shaft. Methods used include: strain gages with slip rings, optical devices, variable inductance transformers, and FM-FM transmitters where a high frequency FM signal is superimposed on an FM carrier.
Each of these methods has a disadvantage. Strain gages with slip rings restrict radial and axial movement or require the use of a floating bearing for brush mounting. Slip rings also introduce unwanted noise into the system and currently limit the maximum rotational velocity to 5000 feet per minute (fpm). Optical devices require very precise alignment and cannot tolerate axial or radial shaft movement. Variable inductance methods require close tolerances around the circumference of the rotating device and cannot tolerate radial movement. The FM-FM technique has been by far the most versatile approach to date. However, because it must operate at a very high frequency, the FM-FM transmitter is very susceptible to frequency instability due to capacitance and inductance variations caused by component flexture at high RPM. Encapsulation of existing devices has only partially mitigated these problems. In addition existing FM-FM devices are available only as strap-on hardware and as such introduce rotational imbanace into the system. FM-FM techniques also require the use of complex FM-FM receivers presently available only in large, rack-mount sizes.